Let's start with a basic understanding of "blackface:"
In the United States the practice gained popularity during the 19th century and contributed to the spread of racial stereotypes such as the "happy-go-lucky darky on the plantation" or the "dandified coon". By the middle of the century, blackface minstrel shows had become a distinctive American artform, translating formal works such as opera into popular terms for a general audience. Early in the 20th century, blackface branched off from the minstrel show and became a form in its own right. In the United States, blackface had largely fallen out of favor by the turn of the 21st century, and is now generally considered offensive, disrespectful, and racist, though the practice continues in other countries where it is not deemed racist or offensive.
Generally offensive it says. However, it is not generally offensive--it's embraced by other parties in a different fashion, "whiteface." Plenty of comedians have acquired the role. See Eddie Murphy first.
This is easily one of the best skits of what it's like to be white. It's not fully true today in many areas, but there are some areas still remaining in the "dark" ages.
This is easily one of the best skits because... well, why not?